Method of producing in seriatim separate coatings on a conductor

ABSTRACT

Selected, spaced regions of a conductor having a continuous, electrically sensitive film coated thereon are subjected to electrolytic deplating to completely remove the film from the selected regions and expose the underlying conductor.

United States Patent 1151 3,639,21 7 Shukovsky et al Feb. i, i972 [54] METHOD OF PRODUCING IN 3,135,671 6/1964 Gade et a! ..204/35 X I T M SEPARATE COATINGS ()N A 3,150,268 9/1964 Montgomery ..204/l43 R X CONDUCTOR 3,189, 32 6/1965 Chow et al. ......Z04/35 X 3,267,0l3 8/1966 Mathias ....204/l43 R 1 Inventors: Harold Barry Shulwvsky, Lawrenceville; 3,328,270 6/1967 Matsushita.... ..204/15 Theodore Elwyn Tomk, Raritan Township, 3,441,494 4/1969 Oshima et a1]. ..204/21 1 Hunterdo" COUmY, of 2,457,234 12/1948 Herbert et al ..204/224 x [73] Assignee: Western Electric Company, Incorporated,

New York, NY. Primary Examiner-John H. Mack Assistant ExaminerR. J. Fay [22] June 1969 Attorney-H. J. Winegar, R. P. Miller and w. M. Kain 211 App]. No.: 832,142

[52] US. Cl. ..204/35 R, 204/15, 204/143 R,

204/206, 204/208, 204/211, 340/174 PW, 340/174 [57] ABSTRACT BA llll- CL C23 5/50, 301R 3/ 01 b 0 Selected, spaced regions of a conductor having a continuous, Field of Search ..204/35 R, 15, 206, 21 l, 208. electrically sensitive film coated thereon are subjected to elec- 2 4/ 143 R, DIG. 5, BI 7, D 174 trolytic deplating to completely remove the film from the 174 BA selected regions and expose the underlying conductor. [56] References Cited 3 Claims, 4 Drawing Figures UNITED STATES PATENTS 2,558,090 6/195] Jemstedt ..204/205 BIO L zo/c W 1 CAPSTAN //2 VARIABLE PULSE VARl ABLE D. C VOLTAGE SOURCE GENERATOR PMENIEB FEB I 1972 3,639,217

L 7'- CAFSTAN VARIABLE Q2031 PULSE i GENERATOR SQE r a? t W VOLTAGE A SOURCE T 205 20 2 J/VVENTUFFE T E. TUFFUK J UR/V METHOD OF PRODUCING IN SERIATIM SEPARATE COATINGS ON A CONDUCTOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of coating conductive articles with a series of separate and discrete films, and more particularly to improved techniques for subjecting a conductive substrate to a selective electrolytic operation wherein a series of separate and discrete magnetizable films may be defined thereon to form a magnetic memory device.

2. Discussion Magnetic memory devices are frequently formed from nonmagnetic conductive substrates plated with remanently magnetizable regions. Such regions may be formed from an electrolytically sensitive material such as permalloy. (The expression electrolytically sensitive material, as used herein, designates a material that can be plated onto or deplated from a substrate that is immersed in a suitably excited electrolytic cell containing ions of such material.) The magnetic regions plated on the substrate serve as storage media for data fed to the memory device.

In one form of such device, the substrate is a conductive, nonmagnetic wire having a diameter of, at most, a few mils. Portions of annular, magnetizable regions having two stable magnetic states and a thickness that is generally one micron or less are plated on the wire. Theoretically, each such portion hereafter called a storage bit is magnetically decoupled from, the adjacent bits, and therefore, acts as a separate storage bit. The two stable, magnetic states of each storage bit can be used to represent the digits 1" and 0, respectively, of binary coded data to be stored in the storage bit.

One prior art process for forming the storage bits on the wire involves electrolytically plating a continuous, annular film of magnetic material on the wire. In use, longitudinally spaced, annular portions of the continuous magnetic film are selectively magnetized to produce the individual storage bits which have virtual rather than physical boundary walls.

Because of the absence of physical walls, the use of this process leads to several problems in maintaining the integrity of the several storage bits on the wire. One such problem is magnetic coupling between adjacent bits through the virtual boundary walls, i.e., the intervening magnetic film. Because of this coupling, the establishment of a particular magnetic state in one storage bit either produces an undesired change, or prevents a desired change, in the magnetic state of the adjacent storage bit. Further, it has been observed that after prolonged use of a particular storage bit, its virtual boundary wall starts to creep" toward the wall of an adjacent storage bit. Ultimately, such creeping of the storage bits virtual wall may cause the adjacent storage bit to function as though it had been assimilated by the creeping" storage bit so that such adjacent storage bit ceases to exist as a separate storage entity.

Newer techniques for forming magnetic memory elements have minimized magnetic coupling and creep by eliminating the magnetic film in the area between adjacent storage bits. This elimination has been accomplished by using selective masking techniques to intermittently, rather than continuously, plate the wire so that the storage bits are physically separated by annuli of masking material, or by an annular open space in the magnetic film where the masking material has been removed. Unfortunately, in practice this latter technique is both slow and costly because of l) the extreme care needed in plating minute thicknesses of the magnetic film on small diameter wires by conventional photo techniques; and (2) the general unsuitability of selective masking for continuous processing techniques.

SUMMARY OF THE INVENTION It is an object of this invention to provide a new and improved method of coating conductive articles with a series of separate and discrete films.

It is another object to provide a new and improved method of continuously forming a series of physically separate electrolytically sensitive coatings of a first material on a substrate of a second material.

It is another object to provide an improved method of con tinuously forming a succession of longitudinally spaced, discrete coatings of electrolytically sensitive magnetic material on an elongated nonmagnetic conductor to produce a magnetic memory device.

With these and other objects in view, briefly, the method of the present invention employs the discovery that a series of discrete coatings may be formed on a conductive article without the necessity of selective masking techniques by first coating the entire article with an electrolytically sensitive film, and then electrolytically deplating the coated article between the regions where the coating is desired at an electrical potential sufficient to completely remove the film from the areas to be deplated.

An illustrative form of the present invention contemplates a method of forming a magnetic device in which an elongated, nonmagnetic conductive wire is provided with spaced, discrete coatings of an electrolytically sensitive magnetic material. The wire is first passed through a first electrolytic cell containing ions of the magnetic material. Within the first cell a DC potential is applied to the wire to plate a continuous film of the magnetic material thereon. The plated wire is then passed through a second electrolytic cell within which a timevarying potential is applied to the plated wire to periodically establish electric fields of an intensity sufficient to completely remove the magnetic material from selected portions of the plated wire.

BRIEF DESCRIPTION OF THE DRAWING The aforementioned and other objects and features of the invention will be apparent from the following detailed description of specific embodiments thereof when read in conjunction with the accompanying drawing, in which:

FIG. I is a fragmentary perspective view of a prior art memory device whose individual storage bits are defined by magnetized portions of a continuous coating on a wire;

FIG. 2 is a fragmentary perspective view of a prior art memory device whose individual storage bits are defined by physically separate magnetic coatings on a wire;

FIG. 3 is a pictorial representation of a plating-deplating apparatus and control circuit suitable for practicing the method of the present invention to produce the memory device of FIG. 2; and

FIG. 4 is a section, taken along line 4-4 of FIG. 3, illustrating in greater detail a portion of the apparatus of FIG. 3.

DETAILED DESCRIPTION While the invention in its broad sense has relevance to the coating of many types of articles having a series of separate and discrete films thereon, the particular form of the invention to be described herein is especially useful in the production of a memory device in which a series of longitudinally spaced, two-state magnetic coatings are plated on an elongated nonmagnetic conductor.

FIG. 1 shows an illustrative, prior art, plated wire memory unit 11 including a wire core 12, upon which is coated a continuous megnetizable film 13. Typically, the core 12 is S-mil beryllium-copper while the film is l-micron permalloy, but other materials may be used.

The film 13 includes a plurality of longitudinally spaced, annular regions 14A-14B which may be magnetized in one of two stable states to define storage bits l6Al6B. As is well known in the art, establishment of a particular magnetic state of each bit (illustratively, the bit 16A) may be effected by passing a first series of electrical pulses longitudinally through the wire core 12 in the direction of arrow 21. Next, a second series of electrical pulses is passed circumferentially around the region 14A in one of two opposite directions (illustrated by arrows 22 and 23, respectively), depending upon the information to be stored. In particular, the direction of the second series of pulses determines the magnetic state of the bit.

The respective bits 16A-16B, of the prior art memory unit 11 being integral with the film 13, have no actual geometric physical boundaries. As is well known, however, the limits of the magnetic spheres of influence of the respective bits 16A and 16B may be defined by virtual boundaries identified in the drawing as magnetic domain walls 17A-18A and 178-188. Adjacent domain walls 18A18B of the bits 16A 16B are separated by a nonmagnetized portion 19 of the film 13.

Despite the presence of the nonmagnetized regions 19 of the film 13, magnetic coupling between the adjacent bits l6A-16B often occurs. This coupling creates mutual interference whereby the magnetization of one bit, e.g., 16A either produces an undesired change in the magnetic state of the bit 168 or prevents a desired change therein. Moreover, prolonged use of the bit 16A may cause its domain wall 18A to creep toward the adjacent wall 188 of the bit 16B across the nonmagnetized area 19 of the film 13. When the wall 18A eventually crosses the wall 188, the integrity of one or both of the bits 16A and 16B is destroyed; that is, for all intents, bits 16A and 163 function as a single composite bit having the characteristics of one of them, thus tolling the usefulness of the other as a magnetic storage entity. Alternatively, the bits 16A-16B may function in some other manner which is undesirably uncharacteristic of them both.

FIG. 2 shows an alternative prior art plated wire memory unit 111 functionally similar to the unit 11 of FIG. 1 but having, in place of the continuous film 13, a plurality of longitudinally spaced discrete magnetic bits or films 116A and 116B (FIG. 2) of length L disposed on an elongated wire 112. The bits of the unit 111 have physically defined boundary walls, e.g., 117A and 118A as opposed to the virtual magnetic domain walls 17 and 18 of FIG. 1. Adjacent walls 118A and 1188 ofthe bits 116A and 1168 (FIG. 2) are separated by regions 119 where only the wire 112 is present. The use of such physically separated bits 116A and ]16B has been found to minimize magnetic coupling and creep of the type described in connection with FIG. 1.

In accordance with the invention, the discrete film memory unit 111 of FIG. 2 may be rapidly and inexpensively formed by a technique using the arrangement shown pictorially in FIG. 3.

A first, conventional, electrolytic cell 201 includes a continuously flowing supply of an electrolyte (from a source not shown) that contains ions of the magnetizable material, illustratively permalloy, of which the bits 116A, 116B, etc., are constituted. The cell 201 is associated with the output of a DC voltage source 202 which applies to the electrolyte a positive voltage and to the wire 112 a negative voltage. The moving electrolyte enters the cell 201 via an inlet 201A and exits from the cell via an outlet 2018. The cell 201 is also provided with a pair of aligned passages 201C and 201D through which the wire 112 moves as it passes through the cell 201 in the direction of an arrow 200. As indicated below, the bare wire 112 emerges from the cell 201 as a continuously coated wire 1 13.

Adjacent the first cell 201 is a second electrolytic cell 203 which is provided with an electrolyte which may be similar to that of the cell 201. The electrolyte in the cell 203 continually flows through the cell from an inlet 203A to an outlet 2038. The cell 203 is also provided with a pair of aligned passages 203C and 203D through which the coated wire 1 13 passes.

Disposed within the cell 203 and immersed in the electrolyte is a conductive loop 204 (FIG. 4) made of a metal inert to the electrolyte within the cell 203, such as platinum. The inner diameter of the loop 204 is made slightly larger than the diameter of the coated wire 113 so that the latter can pass therethrough. As shown best in FIG. 3, the loop .204 is connected to the output of a conventional pulse generator 206 through a lead 207. The generator 206 impresses, between the loop 204 and the grounded coated wire 113, a succession of negative-going pulses 205-205 having an amplitude A, a

repetition period T,, and a duration T all of which are adjustable.

In operation, the bare wire 112 which may be initially wound on a spool (not shown) is pulled over a grounded conductive roller 209 and through the aligned cells 201 and 203 by a suitable capstan 210. The roller 209, and thus the wire 112 carried thereon, is connected to the grounded negative output of the source 202. As the wire 111 passes through the electrolyte in the cell 201, the amplitude of the steady, positive DC excitation voltage from the source 202 is adjusted in a conventional manner so that the wire 111 receives a continuous, l-micron thick coating of permalloy. The coated wire 1 13 then passes out of the cell 201 and into the cell 203. The portions of the coated wire 113 that pass through the loop 204 during the duration T of each negative-going pulse at the output of the generator 206 are subjected to an intense radial electric filed (represented by field lines 221, in FIG. 4) resulting from the high negative potential on the loop during the pulse. Since the electric field in the cell 203 results from the application of an exciting potential of a polarity opposite to the voltage that was applied to the cell 201 to initially plate the wire, such field deplates the coated wire portion passing through the loop 204 during such duration T of each pulse from the generator source 206. However, the portions of the coated wire 113 that pass through the loop 204 during the quiescent portion (T -T of the pulse repetition period at the output of the source 206 will not be exposed to the intense deplating electric field and so will remain plated. The intermittent pulse excitation of the cell 203 during each cycle of the pulse output will thereby deplate the coated wire 113 entering the cell 203 in a corresponding intermittent manner to yield, at the output of the cell 203, a plurality of discrete, physically separate, permalloy films 116 separated by the exposed, nonmagnetic portions 119 of the underlying wire 112.

The length L of the discrete films 116 and the length L, of the nonmagnetized underlying regions 119 will be directly proportional to the pulse duration T and the quiescent portion (T -T respectively, of the output from the generator 206. The degree of deplating the regions 119 during their passage through the loop 204 will be dependent upon the amplitude A of the negative-going pulses. It is important at all times that the amplitude A is adjusted to be sufficiently large such that the entire permalloy coating is removed from the coated wire 1 13 during its passage through the loop 204.

It will be understood by those skilled in the art, that a single electroplating cell may be substituted from the separate plating and deplating cells 201 and 203 in FIG. 3. One manner of accomplishing this is to position a conductive loop (not shown), similar to the loop 204, at the exit end of cell 201 and to connect it to the pulse generator 206 as described above, thus obviating the need for a separate deplating cell.

What is claimed is:

l. A method of delineating a plurality of spaced regions on the surface of a continuous length conductor which is surrounded by a coating that is formed from an electrolytically sensitive material different from that of the conductor; the improvement which comprises:

continuously passing the coated conductor through an electrolytic bath so that the entire surface, coated with the electrolytically sensitive material is immersed in and exposed to the bath; and

intermittently applying a deplating potential to selected spaced regions along the surface of the continuously coated conductor while the entire coated surface conductor is exposed to the bath, and continuously passes through the bath, to completely remove the sensitive material in the spaced regions and expose the underlying surface of the conductor.

2. In a method of forming a series of separate and discrete magnetic coatings on a conductor, the steps comprising:

passing a wire through a first portion of an electrolytic cell containing an electrolyte having magnetic ions;

continuously exciting the first portion of the cell with an electrical potential of a first polarity and an amplitude sufficient to plate a continuous magnetic film on the wire as it passes through the cell;

passing the plated wire through a second portion of the electrolytic cell containing the electrolyte having the magnetic ions; and

intermittently exciting the second portion of the cell in synchronism with the movement of selected areas of the plated wire therethrough with an electrical potential having a second polarity opposite to the first polarity and an amplitude sufficient to completely deplate the selected areas of the plated wire.

3. In a method of forming a series of separate and discrete magnetic coatings on a conductor, the steps comprising:

passing a conductor through a first electroplating cell which contains an electrolyte having magnetic ions and which is connected to a first continuously excited source of EMF of a first given polarity having an amplitude sufficient to plate a continuous magnetic film onto the conductor;

passing said plated conductor through a second electroplating cell which contains a similar electrolyte and which is connected to a selectively excitable second source of EMF; and

pulsing the second source at periodic intervals during the passage of the plated conductor therethrough to intermittently apply to the second cell an exciting potential having a polarity opposite to the first polarity and an amplitude sufficient to completely deplate corresponding intermittent areas of the magnetic coatings on the conductor. 

2. In a method of forming a series of separate and discrete magnetic coatings on a conductor, the steps comprising: passing a wire through a first portion of an electrolytic cell containing an electrolyte having magnetic ions; continuously exciting the first portion of the cell with an electrical potential of a first polarity and an amplitude sufficient to plate a continuous magnetic film on the wire as it passes through the cell; passing the plated wire through a second portion of the electrolytic cell containing the electrolyte having the magnetic ions; and intermittently exciting the second portion of the cell in synchronism with the movement of selected areas of the plated wire therethrough with an electrical potential having a second polarity opposite to the first polarity and an amplitude sufficient to completely deplate the selected areas of the plated wire.
 3. In a method of forming a series of separate and discrete magnetic coatings on a conductor, the steps comprising: passing a conductor through a first electroplating cell which contains an electrolyte having magnetic ions and which is connected to a first continuously excited source of EMF of a first given polarity having an amplitude sufficient to plate a continuous magnetic film onto the conductor; passing said plated conductor through a second electroplating cell which contains a similar electrolyte and which is connected to a selectively excitable second source of EMF; and pulsing the second source at periodic intervals during the passage of the plated conductor therethrough to intermittently apply to the second cell an exciting potential having a polarity opposite to the first polarity and an amplitude sufficient to completely deplate corresponding intermittent areas of the magnetic coatings on the conductor. 